Positively chargeable toner

Abstract

A positively chargeable toner includes a plurality of toner particles each including a toner mother particle and external additives adhering to a surface of the toner mother particle. The toner particles of the positively chargeable toner each include a silica particle as one of the external additives and a titania particle as another one of the external additives. The silica particle has on a surface thereof an alkyl group having a carbon number of at least 8 and no greater than 16 and an amino group. The titania particle has an amino group on a surface thereof. The titania particle has a volume resistivity of at least 1.0×10 9 Ω·cm and no greater than 1.0×10 11 Ω·cm. The silica particles have an average primary particle diameter larger than that of the titania particles.

What is claimed is: 
     
       1. A positively chargeable toner comprising
 a plurality of toner particles each including a toner mother particle and external additives adhering to a surface of the toner mother particle, wherein 
 the toner particles each include a silica particle as one of the external additives and a titania particle as another one of the external additives, the silica particle having on a surface thereof an alkyl group having a carbon number of at least 8 and no greater than 16 and an amino group, the titania particle having an amino group on a surface thereof, 
 the titania particle has a volume resistivity of at least 1.0×10 9  Ω·cm and no greater than 1.0×10 11  Ω·cm, 
 the silica particles have a number average primary particle diameter larger than that of the titania particles, 
 nitrogen atoms are present on the surfaces of the titania particles in an amount of at least 0.01% by mass and no greater than 0.60% by mass relative to a mass of the titania particles, and 
 carbon atoms are present on the surfaces of the titania particles in an amount of at least 2.00% by mass and no greater than 4.00% by mass relative to the mass of the titania particles. 
 
     
     
       2. The positively chargeable toner according to  claim 1 , wherein
 a ratio of the number average primary particle diameter of the silica particles to that of the titania particles is at least 1.1 and no greater than 2.0. 
 
     
     
       3. The positively chargeable toner according to  claim 2 , wherein
 an amount of the silica particles is at least 0.5 parts by mass and no greater than 5.0 parts by mass relative to 100 parts by mass of the toner mother particles, and 
 an amount of the titania particles is at least 10 parts by mass and no greater than 50 parts by mass relative to 100 parts by mass of the silica particles. 
 
     
     
       4. The positively chargeable toner according to  claim 1 , wherein
 the surfaces of the titania particles are hydrophobized. 
 
     
     
       5. A positively chargeable toner comprising
 a plurality of toner particles each including a toner mother particle and external additives adhering to a surface of the toner mother particle, wherein 
 the toner particles each include a silica particle as one of the external additives and a titania particle as another one of the external additives, the silica particle having on a surface thereof an alkyl group having a carbon number of at least 8 and no greater than 16 and an amino group, the titania particle having an amino group on a surface thereof, 
 the titania particle has a volume resistivity of at least 1.0×10 9  Ω·cm and no greater than 1.0×10 11  Ω·cm, 
 the silica particles have a number average primary particle diameter larger than that of the titania particles, and 
 the toner particles each further include an organic particle as another one of the external additives, the organic particles having a number average primary particle diameter of at least 60 nm and no greater than 120 nm and a hydrophobicity degree measured by a methanol wettability method of at least 10% by mass and no greater than 30% by mass. 
 
     
     
       6. The positively chargeable toner according to  claim 1 , wherein
 a first group and a second group are present on the surface of the silica particle and a third group is present on the surface of the titania particle, 
 the first group is represented by a formula (1) shown below, and 
 the second group and the third group are represented, independently of each other, by a formula (2) shown below, 
 
       
         
           
           
               
               
           
         
         where in the formula (1), R 11  represents an alkyl group having a carbon number of at least 8 and no greater than 16, 
       
       
         
           
           
               
               
           
         
         in the formula (2), R 21  and R 22  each represent, independently of each other, a hydrogen atom or an optionally substituted alkyl group, and R 2  represents an optionally substituted alkylene group. 
       
     
     
       7. A positively chargeable toner comprising
 a plurality of toner particles each including a toner mother particle and external additives adhering to a surface of the toner mother particle, wherein 
 the toner particles each include a silica particle as one of the external additives and a titania particle as another one of the external additives, the silica particle having on a surface thereof an alkyl group having a carbon number of at least 8 and no greater than 16 and an amino group, the titania particle having an amino group on a surface thereof, 
 the titania particle has a volume resistivity of at least 1.0×10 9  Ω·cm and no greater than 1.0×10 11  Ω·cm, 
 the silica particles have a number average primary particle diameter larger than that of the titania particles, and 
 the silica particle has a volume resistivity of at least 1.0×10 14  Ω·cm and no greater than 1.0×10 16  Ω·cm. 
 
     
     
       8. The positively chargeable toner according to  claim 1 , wherein
 the silica particle protrudes more than the titania particle on the surface of the toner mother particle.